This disclosure relates generally to methods and systems for color management in image/text printing or display systems, and more particularly to a system and method for automatically achieving spot color production through use of a plurality of gain matrices per spot color in determining spot color coordinates.
To meet customer demand, the commercial printing industry requires the capability of producing spot colors accurately and consistently. Spot colors can be defined as a fixed set of colors which may be Pantone® colors, customer logo colors, colors in a customer's proprietary marked patterns, or customer defined colors in the form of an index color table. Spot colors are often used, or can be used, for large background areas, which may be the most color critical portion of a particular page. Consistent color in these areas may determine the difference between success or failure in meeting customer requirements.
A goal of the disclosed system and method is to transform the current production print practice by providing an automated approach to the printing of spot colors. Because imaging can occur over a variety of different printing systems and practiced by a variety of different clients and customers, the colors may not always be consistent or accurate. Existing spot color editors utilize a manual approach to the adjustment of CMYK recipes of spot colors prior to raster image processing (RIPing). For example, the document creator may select a Pantone color for application in specific areas through a user interface on a printing device or computer monitor, such as that available on the Xerox® DocuSP® Controller. The Pantone-provided CMYK recipe for the selected printer is obtained from a look-up table. Prior to RIPing the document in the printer, the operator has the option of entering a spot color editor function and specifying an alternative CMYK recipe to achieve the desired color. The document is then RIPed and then printed using the spot color editor recipes where specified, and Pantone recipes otherwise.
However, the algorithms used in such prior art devices require the use of a pre-calculated single gain matrix per spot color as inputs. Gain matrices are obtained using the printer Jacobian matrix and MIMO pole-placement algorithms. Since these matrices are calculated offline during the printer characterization process, the convergence of spot colors to achieve desired accuracy can vary depending on the machine state. Also, the state feedback design may not perform as well as desired for colors near the boundary and the deltaE2000 convergence criteria cannot be easily defined while selecting proper gain matrices since the prior art design uses the CIELab convergence criteria. The computation of deltaE2000 number provides an improved method for comparing color differences in perceptual space. Therefore, it is highly desired to establish the convergence criteria in such a way that the deltaE2000 value for each color is minimized using the minimum number of algorithm iterations. Consequently, it would be desirable to have an automated system that provides improved color performance through the use of a plurality of gain matrices per spot color in determining spot color coordinates.
All U.S. patents and published U.S. patent applications cited herein are fully incorporated by reference. The following patents or publications are noted:
U.S. Patent Application Publication No. 2002/0093684 to Bares et al. (“Accurate Printing of Proprietary Mark Patterns and Colors”) describes a printing system that provides a dictionary of recognizable patterns and defined colors corresponding to proprietary marks and selected colors. The dictionary is linked to a user interface on which a user may designate a location within a document and one or more of the proprietary marks with defined colors from an accessible menu. A processor associates the defined colors with the image at the specified location and generates a printer signal representative of the colors and image. Alternatively, the processor may include a pattern recognizer for identifying recognizable patterns within a document. Those patterns having a likeness to defined patterns within the pattern dictionary can be converted to the defined patterns for display or imaging.
U.S. Pat. No. 6,157,469 to Mestha (“Dynamic Device Independent Image Correction Method and Apparatus”) describes a method of controlling color drift between a desired image and an output image as obtained by a marking device and intended to match the desired image. The method includes detecting a current output color in the output image with a color sensing device, determining a difference between the current output color in the output image and a corresponding color in the desired image, and automatically setting a next output color in the output image equal to a corrected color that minimizes the difference between the next output color and the corresponding color in the output image.
U.S. Pat. No. 6,178,007 to Harrington (“Method for Continuous Incremental Color Calibration for Color Document Output Terminals”) teaches a method for continuously upgrading the color calibration for an electrophotographic printer using a color transform look up table stored in memory. A single or small number of color patch samples is printed at regular intervals during the use of the printing machine. The color patches are sensed and a determination made as to the difference between the sensed color and the desired color. A corrective color calibration value is determined for the sensed patch and a correction is made for that color in the printer memory. The process is repeated to assure that all of the colors within the gamut of the machine are continuously updated.
U.S. Pat. No. 6,744,531 to Mestha et al. (“Color Adjustment Apparatus and Method”) teaches an apparatus for providing consistent output across a plurality of different hard copy output devices which may be included in a system having an image data source and a hard copy output device. The image data source supplies image data to a printable image data adjusting apparatus. The image data supplied may be in a device-dependent color space or a device-independent color space. For image data in a device-dependent color space, the adjusting apparatus first converts the image data into device-independent image data and stores it in memory as target image data. If the image data is already device-independent, the image data are stored in the memory of the adjusting apparatus as target image data. The printable image data adjusting apparatus then uses the target image data to generate printable image data. The hard copy output device uses the printable image data to generate a hard copy image. The hard copy image is then passed within the optical field of a sensor that detects device-independent image data values of the hard copy image. The detected device-independent image data values are then compared against the target image data to generate color adjustment factors. The color adjustment factors are used to produce a hard copy image having detected device-independent image data values that more closely represent the target image data.
U.S. Pat. No. 6,809,837 to Mestha et al. (“On-line Model Prediction and Calibration System for a Dynamically Varying Color Reproduction Device”) teaches a method and apparatus for on-line prediction of an analytical model of a dynamically varying color reproduction device. The method includes recursively executing a parameter adjustment algorithm for updating the parameters to the analytical model. Parameter adjustment is computed based upon a measured error signal detected between a sensed signal detected from actual device output and with an insitu sensor, and the analytical model output. The adjustment algorithm is recursively executed until parameter convergence effects a minimal error measurement, at which time the updated parameters are identified as accurate within the selected parametric model.
U.S. Pat. No. 7,069,164 to Viturro et al. (“Method for Calibrating a Marking System to Maintain Color Output Consistency Across Multiple Printers”) teaches a method for maintaining consistent color output across printers even when the inline sensors have differences in accuracy due to various technical and environmental factors. A spectrophotometer is used to measure the color quality of printed references. Adjustments are then iteratively made until reference charts of desired color quality are obtained. The printed reference allows one to achieve relatively high system performance by removing sensor inaccuracies. Using the printed reference measured by the inline sensor, control systems of each machine are calibrated. At customer sites and at suitable intervals, a reference document can be read using the inline sensor on a reference machine and any differences from expected values can be calibrated out.
U.S. Patent Application Publication No. 2005/0030560 to Maltz et al. (“Methods and Systems for Controlling Out-of-gamut Memory and Index Colors”) describes methods and systems in an image processing device for controlling colors that are located external to a gamut. A plurality of color values can be automatically provided as input to said image processing device, wherein the image processing device is under the control of a particular dimensional order, typically a three-dimensional order, but alternatively can be a two-dimensional order. An operation can then be performed dynamically determining which color value among the plurality of color values has attained a gamut limit. Thereafter, the particular dimensional order can be automatically reduced, providing improved control for colors that are located external to the gamut. The plurality of color values analyzed is generally associated with three colors: cyan, magenta, and yellow.
The disclosed embodiments provide examples of improved solutions to the problems noted in the above Background discussion and the art cited therein. There is shown in these examples an improved method of color management for image marking devices utilizing an automated spot color editor having a control module accessing a graphical user interface. The method includes receiving image data input, in either device-dependent color space or device-independent color space, for a marking job. It is determined whether spot colors are present within the image data input and whether the CMYK values for each of the spot colors present within the image data input are included in the marking device spot color dictionary. Operational parameters for the automated spot color editor are initialized, with operational parameters including the desired performance criteria to be minimized by the automated spot color editor through selection of one or more matrices from a plurality of possible gain matrices to identify new CMYK values. The quality level of the new CMYK values is assessed and the new CMYK values are transmitted to an image printing device(s).
In an alternate embodiment there is disclosed a system for color management in image marking devices. The system includes an automated spot color editor having a control module accessing a graphical user interface. The system receives image data input for a marking job, with the image data in either device-dependent color space or device-independent color space. The system determines whether spot colors are present within the image data input and checks whether the CMYK values for each spot colors present within the image data input are included in the marking device spot color dictionary. The operational parameters for the automated spot color editor are initialized, with the operational parameters including the desired performance criteria to be minimized by the automated spot color editor through selection of one or more gain matrices from a plurality of possible gain matrices. The parameters and selected gain matrix(es) are utilized to identify new CMYK values. The system assesses the quality level of the new CMYK values and transmits the new CMYK values to one or more image printing device(s).
In yet another embodiment there is disclosed a computer-readable storage medium having computer readable program code embodied in the medium which, when the program code is executed by a computer, causes the computer to perform method steps for color management in image marking devices through use of an automated spot color editor having a control module accessing a graphical user interface. The method includes receiving image data input, in either device-dependent color space or device-independent color space, for a marking job. It is determined whether spot colors are present within the image data input and whether the CMYK values for each of the spot colors present within the image data input are included in the marking device spot color dictionary. Operational parameters for the automated spot color editor are initialized, with operational parameters including the desired performance criteria to be minimized by the automated spot color editor through selection of one or more matrices from a plurality of possible gain matrices to identify new CMYK values. The quality level of the new CMYK values is assessed and the new CMYK values are transmitted to an image printing device(s).